Process for dehydrating cellulose nitrate



Patented Dec. 21,'l9 37 I V V \V UNITED STATES PATENT OFFICE PROCESS FOR DEHYDRATING CELLULOSE NITRATE David G, Kennedy and Joseph Keen Rulon, Parlin, N. J., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application November 8, 1934,

Serial No. 752,113 a 2 Claims. (01. 260-148) This invention relates to an improved process lowed by a second treatment with undiluted alfor the removal of water from wet cellulose nitrate cohol while the press cake is still under pressure. and its replacement by alcohol. The invention is carried out in its specific em-' In the preparation of cellulose nitrate, raw mabodiment by placing cellulose nitrate after it has terial such as cotton linters is nitrated and when been drowned and the surplus water removed by the nitration is carried to the extent desired, the placing it in a hydraulic press and squeezing out surplus nitrating acids are removed and the nimost of the water contained in the wet cellulosic trated material is at once drowned in water. The material. While the cellulose nitrate is still nitrated material is carried away by the drowning under pressure, a measured quantity of diluted 'alwater to a vat where boiling is conducted to recohol is pumped into the press and forced through 10 move excess acid. Several changes of water are the press cake, thereby replacing the water which used in this process. The water wet nitrocelluremains in the material.

lose is then delivered to another operation for As the diluted alcohol enters the press cake, the

water removal. water and some of the alcohol are removed at the When the cellulose nitrate is to be used, this same time through the discharge line at the base water must be removed so that a cellulosic me.- of the press. Following this treatment with diterial may be dispersed in solvents with which luted alcohol, a measured quantity of undiluted water is usually incompatible. In the present alcohol is pumped into the press and forced practice the water is usually replaced by an althrough the press cake, so that the diluted alcohol which subsequently forms a part of the cohol contained in the cake is replaced by the 20 dispersing medium. One commercial method stronger alcohol. The alcohol thus diluted and used at present for the dehydration operation is part of the stronger alcohol is collected in a as follows: measuring tank for re-use as the diluted alcohol The cellulose nitrate, which contains from '20 described heretofore. This undiluted alcohol is to'30% of water, is mixed with four or five times usually 95% strength by volume, and after the its weight of 95% alcohol and the slurry placed diluted alcohol is washed out of the press cake,

in a centrifuge to remove the excess alcohol. that which remains is approximately 90% by This step is usually repeated untilalcohol of a volume.

fairly high strength remains in the cellulose ni- The apparatus used may be a hydraulic presstrate. Ordinarily, the treatment is adjusted so of conventional design or it may be specially 30 that the cellulose nitrate contains about 30% of adapted to the process, as will be apparent to its Weight of c o which ru s abo t those skilled in the art; for example, the drain Another procedure commonly used is one in valve may be connected by a lever to the inlet which a specially adapted hydraulic press is emvalve so that one motion will open both valves ployed. In this procedure the water wet celluat the same time. The position of the measuring 35 lose nitrate is placed in the cylinder of the press, tanks, pumps and connecting lines may be placed and the material pressed until the press cake conin any convenient position, as will be readily tains approximately 30% of water. Alcohol iS understood by those familiar with the operation then forced through the press cake until the of hydraulic presses. I

water is replaced to the desired extent by the The process herein disclosed is used for the de- 40 a o o o h of these Ope o s a o ew hydration of cellulose nitrate as commonly emcostly, due to the large amounts of diluted alployed in the various arts. Asexamples, although cohol obtained from the operation. The recovery not limits, of such uses may be mentioned the and rectification of the alcohol in these methods manufacture of smokeless powder, lacquers of e adds greatly to the cost of the process. various types, adhesives, plastics, various types of 45 This invention has as an object a method which coating compositions for coating fabrics or other provides for the removal of water from the wet non-rigid bases, artificial fibers, photographic and cellulose nitrate in such a manner that less dicinema film bases, and other arts where cellulose.

, luted alcohol is obtained. A further object is the nitrate is commonly used.

provision of a method which reduces the loss This invention presents as an advantage over 50 of cellulose nitrate, due to its solubility in the dethe present practice for the dehydration of celluhydrating medium, to a minimum. lose nitrate a reduction to about one-half the These objects are accomplished by treating the amount of alcohol used for a given amount of wet cellulose nitrate under pressure with diluted cellulose nitrate. A further advantage is that the alcohol obtained from a previous treatment, foluse of the diluted alcohol from the second step of 55 Cit the treatment of one batch of press cake for the first treatment of a subsequent press cake greatly reduces the amount of alcohol which is necessary. The economic aspects of these advantages and the saving in the cost of rectifying smaller quantities of alcohol is readily apparent. A still further advantage in the present invention is the increase in yield of dehydrated cellulose nitrate due to the fact that several types of this material are somewhat soluble in 95% alcohol. Losses occur in the ordinary procedure used at present where undiluted alcohol comes into immediate contact with the cellulose nitrate. This is avoided in the present invention by the use of dilute alcohol in the first treatment. A still further advantage is the amount of cellulose nitrate dissolved in the alcohol having been reduced to a minimum, less alkali is necessary in the subsequent rectification and recovery of the washings.

As many apparently widely diiferent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appended patent claims.

We claim:

1. In the process for preparing cellulose nitrate in which the nitrated cellulose material is drowned in water and the surplus water removed, the improvement of replacing the remaining water by ethyl alcohol which comprises washing under pressure the wet cellulose material in the form of a press cake first with ethyl alcohol containing a comparatively large amount of water and then with approximately 95% ethyl alcohol until the water in the nitrated cellulose material has been replaced with about 90% alcohol, collecting the diluted alcohol from the second treatment and washing under pressure the original water wet nitrated cellulose with this alcohol in the first stage of a subsequent run.

2. The process for removing water from wet cellulose nitrate which comprises treating the water-wet cellulose nitrate under pressure with ethyl alcohol containing a comparatively large amount of water and then washing under pressure the cellulose nitrate with about 95% ethyl alcohol whereby the original water in the cellulose nitrate is replaced by approximately 90% ethyl alcohol, collecting the diluted alcohol from the second treatment, and washing under pressure a fresh mass of cellulose nitrate with the said diluted alcohol as the first stage of the subsequent run.

DAVID G. KENNEDY. JOSEPH KEEN RULON. 

